1. Visit example URL (http://jsfiddle.net/54fAZ/)
2. Inspect the div in the result box, and open the Metrics view.
In the Elements/Metrics pane, the content box of the diagram is marked as 50x50 -- the content box is actually 10x10, the border box is 50x50.
Created attachment 90019 [details]
[PATCH] Suggested solution
Committed r84135: <http://trac.webkit.org/changeset/84135>